The field of my invention is mineral processing, and more particularly gravimetric separation devices and methods for separating, concentrating, or recovering mineral values from a feedstock.
The term “values” is used herein to mean the target mineral or minerals that one who is employing my invention wishes to recover or concentrate. The term “gangue” is used herein in its standard mineralogical context to mean the contaminants or non-value components of a feedstock; i.e., the unwanted material in the feedstock from which the values are being separated. The term “feedstock” is used herein to mean a raw mixture or conglomeration made up of values admixed with gangue. Within the context of the present disclosure, a feedstock includes such a mixture that has been screened or otherwise sized. “Fluidized feedstock” and “feedstock slurry” refer to a feedstock suspended in a sufficient volume of processing-fluid, normally water, to facilitate gravimetric separation of values from gangue. Although the present disclosure focuses on gold recovery, my invention and the principles, devices, and processes discussed herein are more generally applicable to all situations were differences in the densities in ores, minerals, and other materials are exploited in order to separate values from gangue.
In the field of mineral processing it has long been known that differences in the densities of minerals and materials can be exploited to separate values from gangue. Gravimetric principles are the basis of many mineral processing techniques, from the primitive gold panning technique to more sophisticated and mechanized techniques such as vibrating or percussion tables, often implemented as “wet tables” that process fluidized feedstock.
The best known approach to wet vibrating tables is the so-called Wilfley table, which is an essentially planar, tilted surface with a plurality of ribs or riffles protruding from the surface. The feedstock is added as a slurry at the high end of the tilted surface and is washed across the surface while a vibrational motion is applied to the table in the plane of the table and orthogonal to the direction of the flow of water. A number of variations of this basic approach have been patented, including differing table shapes and dimensions, different riffle patterns and sizes, different mechanisms for vibrating the table. See, for instance, U.S. Pat. No. 4,758,334 to Rodgers, U.S. Pat. No. 4,078,996 to Cohen-Allror and Cuviller, and U.S. Pat. No. 4,150,749 to Stevens.
Whilst the vibrating table approach has been very useful, improvements in this approach have generally not focused on maximizing the type of motion that is imparted to the feedstock slurry. The motion that has been almost universally used is a vibration, which is to say a to-and-fro lateral motion applied within the plane of the table. An exception to this general simple lateral vibration approach is the 1915 Great Britian patent 9153 to Ogle et al. in which a sudden downward jolt or “vertical bump” is applied to the table.
I have made the discovery that the separation of values from gangue is greatly enhanced by subjecting a washed feedstock or feedstock slurry to a compound cyclic motion, as that motion is defined below. Furthermore, the separation can be enhanced even more by applying the compound cyclic motion to a vee-table that is tilted at an optimum angle, as disclosed herein.
The following definitions are employed throughout this disclosure and the claims.
“Table” is used herein to mean a surface or receptacle element of the invention that receives feedstock for processing. The term includes analogous terms used in the art, by way of example: “pan,” “jig pan,” “trough,” “buddle,” “deck,” “board,” and “riffle board.” A table may have any shape and dimensions that can be employed by my invention. The term “vee-table” refers to an elongate table having sides that converge at the bottom to form a valley that is parallel with the working axis of the table.
“Horizontal” and “vertical” have their common meanings and are used to denote orientation or movement with respect to the ground. The “working axis” of the table refers to the axis of the table parallel to the direction the values and/or gangue migrate when the invention is in operation, which will be along the long axis of elongate tables. “Rectilinear” means along or in the direction of the working axis. “Orthogonal” refers to the direction or orientation that is horizontal and perpendicular to the working axis.
The “tilt-angle” is the angle between horizontal and the working axis. When the two axes are parallel, the tilt-angle is 0 degrees. “Tilt-means” refers to mechanisms disclosed herein and their equivalents that produce a tilt-angle with an absolute value greater than 0 degrees.
“Compound cyclic motion” is defined herein as a motion that combines a reciprocating, rectilinear, to-and-fro motion that is parallel to or coincident with the working axis with a simultaneous, continuous, smooth, vertical up-and-down motion. By “smooth” is meant that there are no sudden vertical movements such as jolts, jarring, or bumps, which tend to stir and re-mix the values and gangue as they separate.
“Table-drive means” refers to mechanisms disclosed herein and their equivalents that impart a compound cyclic motion to a table.